1. It's directed by Matthew Vaughn.
Vaughn was originally going to direct X-Men: The Last Stand, but later pulled out because of (supposedly) he didn't want to be far from his family. As we all know, the same reason was given by Darren Aronofsky after he left The Wolverine. Last year, Vaughn directed the breakout action/comedy film Kick-Ass, with it getting mainly positive reviews (with some going as far as to say that it's one of the best CBMs of all time), despite containing controversial content. I've even heard some people say that Vaughn can't do a bad movie, so why is X-Men: First Class getting all sorts of hate? Fox is apparently letting him do it, and as long as they don't screw anything up, Vaughn will deliver a film that will satisfy those who enjoyed his previous outings.
2. It's produced by Bryan Singer.
Say what you will about his not handling Superman Returns as well as he could have, Singer gave us two X-Men films that many were satisfied with (with X2 gaining very positive reviews and was quite a box office success as well), and wasn't involved with two films that everyone hated. If he can bring to his production skills what he brought to the first two X-films, then I can see some promise coming.
3. It won't focus on Wolverine for a change.
Don't get me wrong, I love Wolverine far more than any other X-Men character, but it seemed like, in the previous X-Men films, that the focus was too much on him instead of the team as a whole. Now that Wolverine's out of the picture, we can focus on characters that haven't had much focus into their background (Mystique, Beast, and of course Magneto and Xavier).
On another note that could be classified under this reason, many people have complained that Cyclops and Jean Grey won't be in this film. I personally am in the majority that both characters should've had some part in the film, but at the same time, it might be beneficial so we can have more screen time with new characters like Emma Frost, Banshee, Havok, etc. who haven't been in film before.
4. The casting seems to be solid so far.
James McAvoy looks similar to a young Patrick Stewart, while Michael Fassbender so far fits in like a glove as Magneto. Although kind of old for the role, January Jones looks great as Emma Frost, while Jennifer Lawrence and Nic Hoult seem just fine as their respective characters. I don't think the casting is something to be worried about in this movie.
5. We'll finally see the origins of Magneto, Xavier, etc. told on the big screen.
One of the grips I've had with the first X-Men film is that (tying in with reason #3) the story only followed Wolverine and Rogue and their finding their way into the X-Men, instead of starting completely from scratch to tell the entire team's origin, the beginning of Xavier's rivalry with Magneto, etc. Now, with X-Men: First Class and its announced sequels, we can finally see the events that led up to the war between the X-Men and Brotherhood in film form.
6. X-Men Origins: Wolverine's timeline won't interfere with the rest of the X-films.
Although I enjoyed Wolverine, its timeline was undeniably screwed over when it came to the X-Men film universe (especially concerning Emma Frost). According to Singer, the film's timeline will be ignored when it comes to the rest of the film series.
7. Screenwriters from Kick-Ass and Thor have written the script.
As stated before, Kick-Ass has been received with many good reviews, and Thor (while not in the US just yet) has had nearly unanimously positive reviews since its recent world premiere. Having screenwriters from both films should be a CBM fan's dream.
8. The film has been compared to Batman Begins by Vaughn.
Ah yes. Ever since its release, nearly every CBM with origins have been compared to Batman Begins, usually near the top of lists containing the greatest CBMs of all time. If X-Men: First Class will be anything like it, then it might have similar success.
9. Vaughn modeled the film after Star Trek (2009).
The 2009 reboot of the Star Trek was met with universally positive reviews upon release (and I still consider it one of my favorite films of all time). Vaughn had First Class modeled after the film by taking the franchise in a new direction with a fresh, young cast. Again, if First Class is anything like what it's been compared to/modeled from, it should be good.
10. Even Vaughn himself has attacked the film's poor marketing.
This is a bit of a minor reason, but I wanted to bring it up anyways. After the release of those embarrassing posters featuring Magneto and Xavier's silhouettes with Fassbender and McAvoy's faces onto the lower parts of their bodies, Vaughn lashed out asking "WTF is this s**t?". Then we got the two theatrical posters this week, which got slightly better reception but criticized the use of Photoshop on the characters' placements between the two posters.
So there, those were a few reasons I brought up in hopes of bringing more appeal to this movie. It's a matter of opinion when it comes to whether or not the movie will be good, but honestly I've been tired of all the hate comments when I don't believe it deserves it. We'll see how it fares on June 3rd.